Re: Can we make $& better?

There is a difference:

$\ = "\n";

my $s = 'abcdefghij';
$s =~ /def/;
print $&;                                # def
print substr($s, $-[0], $+[0] - $-[0]);  # def

$s = '1234567890';
print $&;                                # def
print substr($s, $-[0], $+[0] - $-[0]);  # 456
[download]

Does it matter? Maybe. Switching could break existing code.

Comment on Re: Can we make $& better? Download Code

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Re^2: Can we make $& better? by Anno (Deacon) on Sep 06, 2007 at 19:40 UTC
The difference you point out is even more blatant in this example: `$\ = "\n"; my $s = 'abcdefghij'; $s =~ s/def/123/; print $&; # def print substr($s, $-[0], $+[0] - $-[0]); # 123` [download] Some code is surely using that. The problem with $& and friends isn't the location of the partial strings but the semantics that require copying the parts. Thus for every match, the entire string must be copied. Anecdote: A poster on clpmisc complained that his program "stopped working" after he introduced `use English`. He was matching a short pattern against some monster genome string (one or two GB) with a reasonable number of matches (some 10_000). Copying killed the cat, to coin a phrase. Anno	[reply] [d/l] [select]

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Re^2: Can we make $& better?
by Anno (Deacon) on Sep 06, 2007 at 19:40 UTC

$\ = "\n";

my $s = 'abcdefghij';
$s =~ s/def/123/;
print $&;                                # def
print substr($s, $-[0], $+[0] - $-[0]);  # 123
[download]

The problem with $& and friends isn't the location of the partial strings but the semantics that require copying the parts. Thus for every match, the entire string must be copied.

Anecdote:

A poster on clpmisc complained that his program "stopped working" after he introduced use English. He was matching a short pattern against some monster genome string (one or two GB) with a reasonable number of matches (some 10_000). Copying killed the cat, to coin a phrase.

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